In general, surprise me.
I have my own ideas about how the percentile abilities work but I want to avoid codifying them too much. And you'll find I'm willing to be persuaded by your cunning, clever or crazy rationales for using the skills.
Outside of combat you aren't obligated to automatically roll just because there's a relevant skill. If you just want to tell me what you say or do that's cool -- If I decide a dice roll is required I'll let you know.
While it's perfectly acceptable to just throw dice on a skill you feel is appropriate, feel free to include any description of what specific action you're taking as well. It's possible you may hit on something that will help your roll -- maybe even make it unnecessary.
Social skills based on Intelligence and Leadership should be mainly role-played -- go to the dice if you want to get a little extra oomph but success or failure isn't necessarily going to be determined purely by the roll.
Combining skills is acceptable: "Using Robot Friend and See the Future I attempt to re-calibrate Rollo the Craps-bot to always roll boxcars." It's probably best to limit yourself to using one or two ability rolls per round or action though
On the other hand if you want to do something truly outlandish -- "I Command my Monster Friend Godzilla to roll over and play dead" -- I think throwing the dice is a fun option. Something like this would only work on a ridonkulously good roll, but if you succeed, hey, you just made Godzilla your puppy. How Airwolf is that?
Critical Successes and Fumbles:
At JM's option a roll of 99 or 100 on any percentile check may result in a critical fumble: pratfalls, foul-ups, stubbed toes, broken bones, public humiliation, private shame, and similar mishaps. If the Ability chances are 99 or better a fumble may still occur on a 99 or 100 -- you're so awesome that you only fail spectacularly.
Similarly any percentile roll of 01 or 02 may be a critical success determined by the JM, unless the success chances are only 02 or less, in which case the player should just be glad of his or her good luck to make the check at all.